Chromate treatments are presently being used for the most part in the industrial surface treatment of aluminum coils. Typical examples of chromate treatments include chromic acid chromate conversion treatments and phosphoric acid chromate conversion treatments. Chromic acid chromate conversion treatment solutions were put to practical use around 1950 and are still widely used for fin members and the like in heat exchangers. This chemical conversion treatment solution consists primarily of chromic acid (CrO.sub.3) and hydrofluoric acid (HF), with a promoter added, and forms a film containing some hexavalent chromium. Phosphoric acid chromate conversion treatment solutions are based on the invention in U.S. Pat. No. 2,438,877 from 1945. This chemical conversion treatment solution contains chromic acid (CrO.sub.3), phosphoric acid (H.sub.3 PO.sub.4), and hydrofluoric acid (HF). The film that is formed consists primarily of hydrated chromium phosphate (CrPO.sub.4.4H.sub.2 O). Since the film does not contain hexavalent chromium, it is widely used at present for the paint undercoating treatment of beverage can bodies, particularly drawn and ironed aluminum cans and lids. However, in the interests of environmental protection, a need has arisen for surface treatment solutions which contain no chromium. In recent years, the painting or lamination following such surface treatment has been followed by an increasingly wide range of shaping processes, with the need for increasingly stringent levels of processing, but films made from inorganic systems such as chromate suffer from problems; e.g., the film is broken when bent sharply, preventing adequate performance from being realized, and the like. There is thus strong demand for the development of a technique for forming a flexible film with better corrosion resistance and/or adhesion in articles of manufacture that are shaped after the conversion coating is formed.
Treatment solutions or methods intended to provide the surface of aluminiferous metals with corrosion resistance and paint adhesion using a water-soluble resin have been proposed in Japanese Laid-Open Patent Applications 61-91369, 1-172406, 1-177379, 1-177380, 2-608, 2-609, and others. In these conventional treatment methods, the metal surface is treated with a solution containing a derivative of a polyhydric phenol compound. Problems in these conventional methods, however, are that it is difficult to form a sufficiently stable film in a short period of time on the surface of aluminiferous metal materials, and adequate corrosion resistance cannot be obtained.